The Leyland National single deck bus was developed as a joint venture between British Leyland and the National Bus Company during the late 1960's. The First production examples entered service in the early 1970's, and soon became the standard single deck bus for almost all the National Bus Company fleets.The modular design of the National allowed for easy modification of the vehicle spec, allowing various lengths and door options to be produced.The original Leyland National design was updated during the early 1980's resulting in the National mark II.The earliest production vehicles had a large roof mounted air conditioning pod which was soon replaced by a more compact version.